Communication system



1947- J. R. DESVCH EI'AL 2,425,307

COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Shee'ts-Sheet l I m J Joseph R. Dsch Robert E. Mumma and Ernest V. Gulden Inventors Their A ttorng 1947- J. R. DESCH ETAL 2,425,307

COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 2 Their Attorney 1947. J. R. DESCH EI'VVAL 2,425,307

COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 3 Joseph R. Desch Robert E. Mumma and Ernest V. Guldcn Inventors Their Attorney Cog/78 1947- J. R. DESYCH ET AL 2,425,307

COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 4 Joseph R. Desch Robert E. Mumma and Ernest V. Gulden Inventors W 0 Their Attorney g- 12, 1947- J. R. DESCH ETAL COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 5 J R. Descll R E. Mum: and

Ernest V. Guldu lnvontorn Their Attorney Alll 'VVV

Aug. 12, 1947.

J. R. DESCH ET AL 2,425,307

COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 6 .L I '5 T I i Z2 42 a -95 93, 94 /.05v 5 6 i 52 "v /40 /4Z /43 Joseph D I /50v Robert E. Mumma and M A By W Their Attorney Aug. 12, 1947. J. R. DESCH ET'AL 2,425,307

COMMUNICATION SYSTEM Filed Sept. 16, 1 42 14 Sheets-Sheet 7 Aug. 12, 1947. J. R. DESCH EI'AL COMMUNICATION SYSTEM 14 Sheerls-Sheet 9 Filed Sept. 16, 1942 Joseph R. Desch Robert E. Mumma and b jwmw W m W W W w v Q mm W W m n W m m m m "m m w n n l l mm m H mm M 1 A A m m g 2 w L? m i v v n" 7 v" u MI I 1 M m D PIPE a u n 1 1 1 1 1 1 D1 1 1 1D1'1D1D1P 1I1D1D1D1D VI fig 5% m I n 111 11 u H k m 0 H H H m m m n 3 Ernest V. Guldcn Inventors w m o R A r M T Aug. 12, 1947. J. R. DESCH ETAL 2,425,307

COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 12 g? FIG-.12

g 53/ Joseph R. Dcsch Robert E. Mumma and Ernest V. Guldcn GP [05 v 2 9 0v Inventor! Their Attorney mg. 1, 1947. J. R. DESCH ETAL.

COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 13 v \R 8n 7 7 mam s QR 5W 3% 3% Aug. 12, 1947. J. R. DESCH EIAL COMMUNICATION SYSTEM Filed Sept. 16, 1942 14 Sheets-Sheet 14 FIG.14

SPACE Patented Aug. 12, 1941 2.425.301 COMMUNICATION SYSTEM Joseph R. Desch, Ernest V. Gulden, and Robert E. Mumma, Dayton, Ohio, assignora to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Application September 16, 1942, Serial No. 458,546 I 18 Claims. (Cl. 177-358) This invention relates to communication systems and is directed particularly to a system in which various symbols making up the data to be transmitted are transformed into bursts or trains of discrete rapidly recurring signals, the number of signals in each burst being dependent upon the symbol which it represents. The :bursts representing the different symbols are sent one after another over a single communication channel, and a marking signal is provided for each burst to indicate the completion oi. the burst. The marking signal is used to control a receivin apparatus to govern the allocation and storage of the symbols therein. The signals by which the symbols may be represented may take various forms, as, for instance, interruption or. modulation of a continuous carrier wave and/or dis-' crete rapidly recurring impulses, or representations thereof.

The sending apparatus is provided with means for generating the bursts of signals and controls the number of signals in each burst according to the symbol being sent. The signals can be transmitted by any convenient means; for instance, over a wire or by radio to a receiving and storing apparatus, where they are transformed back into single representations of the symbols and are stored.

The receiving apparatus contains a plurality of transforming and symbol-storing means, each consisting of a group of devices, which transforming and symbol-storing means may be selectively and successively rendered efiective under control of the marking signals to receive the symbol-representing signals and which devices of a group represent the symbols and are differentially operated according to the number of signals in a burst to transform the signals back into a single or direct representation of the symbol and to store this representation.

The receiving apparatus responds to the signals when they are received, and, since it is the number of signals and not their position in a fixed cycle which is the controlling factor, there is no need to synchronize the operation of the sending and receiving apparatus either before or during a transmitting operation.

High-speed communication of data is obtained with applicants novel arrangement because the sending and receiving apparatus can generate and respond to the signals at a high frequency and because the signal bursts which are used to represent the various symbols require only the time necessary to produce the number of signals needed to represent the symbols and can follow one after the other in transmission without unnecessary loss of time between bursts.

Furthermore, there is no particular sequential relation between the various symbols and the number of signals which may be used to represent them, so that the number of signals which represent any symbol may be chosen arbitrarily. Because of this condition, the symbols used most frequently can be represented by the smaller number of signals, and this will also reduce the time required for transmitting data.

It is an object of the invention, therefore, to provide novel high-speed means for sending and receiving data in the form of bursts of diflerent numbers of signals.

.A further object of the invention is to provide a means for producing bursts of signals, each burst comprising a predetermined number of symbol-representing signals followed by a control signal.

A further object of the invention is to provide a novel means for transforming a data-representing symbol into a number of discrete rapidly-recurring signals.

A further object of the invention is to provide a means to transform any data-representing symbol into a signal train comprising a number of discrete signals of one type for indicating the symbol and a control signal of another type for indicating the end of the signal train,

A further object of the invention is to provide a means upon which may be set a plurality of symbols comprising data to be transmitted, which symbols are transformed one after another into bursts cfdifierent numbers of like discrete signals representing the symbols and are sent out over a single communication channel.

A further object of the invention is to provide a means to transform a plurality of data-representing symbols into bursts or individual trains of diiierent numbers of discrete signals corresponding to the symbols, with a marking signal included in each burst to distinguish the bursts.

A further object of the invention is to provide means for receiving different numbers of discrete signals which represent symbols and transforming the signals into a representation of thesymbols.

A 'further object of the invention is to provide a receiving means for receiving bursts of signals consisting of signals having one characteristic and signals having a distinctive characteristic, and having discriminating means to distinguish between the signals having different characteristics and to control the receiving means accordingly.

A further object of the invention is to provide a means for receiving and transforming bursts of symbol-representing signals into direct representations of the various symbols, each of said bursts containing a number of similar discrete signals and a control signal, and said receiving means containing a plurality of transforming means for setting up direct representations-of the various symbols according to the number of lignals in a burst and a routing means controlled by the control signals to route the bursts to the different transforming means.

With these and incidental objects in view. the invention includes certain novel features of construction and combinations of parts, the essential elements of which are set forth in appended claims and a preferred form or embodiment of which is hereinafter described with reference to the drawings which accompany and form apart of this specification.

In the drawings:

Fig. 1 shows a portion of a set of keys for setting up a symbol in the sending apparatus and a portion of the symbol-transforming means controlled thereby for controlling the number of impulses which will be sent to represent the symbol set up on the keys.

Figs. 2 to 5 inclusive are similar to Fig. 1, and together with Fig. 1 provide means for setting up and controlling the sending of five symbols in succession.

Fig. 6 shows the start and stop controls for the sending apparatus, and also shows the mean for forming the symbol-representing impulses and the marking signals.

Figs. 7 to 11 inclusive show portions of the transforming and symbol-storing means in the receiving apparatus, which means consists of groups or banks of symbol-representing tubes which may be selectively set according to the symbols corresponding to the impulses sent by the sending apparatus.

Fig. 12 shows relay means for selectively directing or routing impulses to the various groups of transforming and symbol-storing means.

Fig. 13 shows a routing control device containing a plurality of sequentially operable tubes which are controlled by the marking signals to control the relay means which route the impulses representing various symbols into the proper groups or banks of transforming and symbolstoring means.

Fig. 14 shows means in the receiving apparatus for discriminating between symbol-representing impulses and marking impulses and controlling the receiving apparatus according to the significance of the impulses.

Fig. 15 shows five bursts which may be transmitted in succession and illustrates the general character of the trains of signals by which the symbols are transmitted.

Grnzasi. Dascarprron The symbols which may be sent and received by the novel apparatus may represent any selected data such as the digits of numerical notation, the letters of the alphabet, or any other arbitrary data which may be chosen.

The disclosed embodiment is shown with a capacity for automatically transmitting five symbols in succession and is arranged to transmit the letters of the alphabet.

For the purposes of this disclosure, the signals by which the symbols are represented will consist of discrete rapidly recurring impulses, and these impulses will be transmitted from the sending apparatus to the receiving apparatus over a wire. However, it is not intended to limit the invention to this particular form of signal and transmission medium, as the invention is capable of being carried out by using other equivalent arrangements.

The sending apparatus contains five groups or banks of keys. The keys of each group represent a space symbol and the letters A to Z and are used for setting up symbols to be' trammitted.v

Associated with each bank of keys is a bank of Baseous electron tubes which contains a tube corresponding to each symbol represented by the keys, and, in addition to these tubes, contains a marking impulse tube and a shift tube.

The tubes of each bank control the number of impulses which will be in a burst and are connected in a chain to be fired automatically one after another in sequence, beginning with any selected symbol-representing control tube in the chain and continuing through the marking impulse tube to the shift tube. The depressed key in any bank selects the starting point in the firing sequence by preparing its related symbol-representing control tube to be fired in response to an impulse commonly impressed on all of the symbol-representing control tubes. Once a tube in a bank is fired, it will start the automatic firing of the other tubes in the sequence one after another until the shift tube is fired and becomes conducting. By mean of these tubes, the symbol is transformed into a series of rapidly recurring impulses. The symbol-representing control tubes are connected to an impulse line and send an impulse over the line each time one of the tubes i fired, and these impulses are utilized to control the output of a small-amplitude impulse generating tube which sends out a small-amplitude impulse to the receiving apparatus each time one of the symbol-representing control tubes is fired.

When the last symbol-representing control tube in a chain is fired, it causes the marking impulse tube to fire. The marking impulse tube sends an impulse to control a second impulse generating tube, which sends to the receiving apparatus an impulse having a larger amplitude than the impulses sent out under control of the symbolrepresenting control tubes. The impulses from the small and large-amplitude impulse-generating tubes are impressed on a single output conductor and may be sent to the receiving apparatus.

The marking impulse tube, when it is fired. causes the shift tube of this bank to be fired and send an impulse to the symbol-representing control tubes of the next bank of the tubes to fire the prepared symbol-representing control tube therein and start sequential firing of the tubes of that bank. By means of the shift tubes, various I banks of tubes are rendered operative one after another in succession, and this successive operation of the banks of tubes enables the symbolrepresenting control tubes of all the banks to control the same small-amplitude impulse-generating tube, and the marking impulse tubes of all the banks to control the same large-amplitude impulse-generating tube so that the impulses representing the different symbols can be sent in succession over a single communication channel. The output from these generating tubes will therefore consist of bursts of rapidly recurring impulses for each bank of tubes, each burst being made up of a series of small-amplitude impulses followed by a large-amplitude impulse.

It is clear that the invention is not limited to the use of small-amplitude impulses as the plurality of signals, and large-amplitude impulses as terminal signals, because the large-amplitude impulses couid obviously be used to make up the plurality of signals, and the small-amplitude impulses could be used as terminal signals.

A delay is provided in the firing of the shift tube of each bank by its related marking impulse tube. This delays the initiation of the firing of the tubes of the next bank and provides a space or time interval between the successive bursts.

After the symbols have been set up on the keys, transmission of the symbols is initiated by operating a start key, which causes a firing impulse to v be sent to the symbol-representing control tubes of the first bank of tubes to start the sequential firing of the tubes therein. The remaining banks 01' tubes will be rendered operative automatically in succession, and the shirt tube of the last bank will cause the termination of the transmitting operation.

The receiving apparatus contains a discriminating means which receives the impulses and is capable of distinguishing between the smallamplitude and the large-amplitude impulses; a routing means; and a plurality of transforming and symbol-storing means consisting of groups or banks of gaseous electron tubes for transforming the bursts of impulses into single representations of the symbols and storing the symbols.

Each group or bank of transforming and symbol-storing tubes contains a tube representing each symbol, a tube corresponding to the marking impulse, and a pre-setting tube. The marking impulse and symbol-representing tubes of each bank are connected to be fired one after another in response to the impulses sent out by the sending apparatus, the order of firing beginning with the marking impulse tube, then the space symbol tube, and next the tubes for the symbols A to Z, which, it will be noted, is exactly the reverse order of the firing of the tubes in the sending apparatus. As each tube in the bank is fired, it extinguishes any previously conducting tube in the bank, and this means that only one tube will be conducting in each bank at the end of a receiving period and these conducting tubes in the various banks will correspond to the symbols received. The conducting tubes will continue to conduct after'the receivin eriod and serve as a means for storing the symbols.

As explained earlier in connection with the sending apparatus, the bursts of impulses representing the various symbols are sent out one after another in succession over a single wire, and, because of this,vrouting means must be provided in the receiving apparatus to distribute or allocate the bursts to the proper banks of transforming and storing tubes. The particular routing means shown herein includes a normally inoperative relay means for each bank of tubes, which relay means may be selectively rendered effective one after another to relay the bursts of impulses from a common impulse line to the various banks of transforming and storing tubes,

The relay means are rendered effective one after another by means of a routing control device consisting of a series of gaseous electron tubes which are connected in a chain to be fired and rendered conducting one after another in sequence in response to the marking impulses. The tubes of the routing control device are also connected so that the firing of any tube in the chain will cause any previously conducting tube of the chain to be extinguished and allow only one tube at a time to be conducting. The chain connections and extinguishing connections between the routing control tubes, therefore, enable the tubes to become conducting one at a time in sequence, and, as long as any tube is conducting, it renders its associated relay means operative to relay impulses from the common impulse line to its associated bank of transforming and symbolstoring tubes.

While the routing means is shown as. consisting of a plurality of relays, it is obvious hat the routing means could take other forms. such as a sequence switch which is capable of step-by-step operation to relay the impulses to the various banks. The discriminating means in the receiving apparatus receives all the impulses which are sent from the sending apparatus and includes means which is responsive to both smalland largeamplitude impulses and means which is only responsive to the large-amplitude impulses. The means which is responsive to all the received impulses passes these impulses to a common impulse conductor in the receiving apparatus, from which conductor the impulses are relayed selectively to the various banks of transforming and symbol-storing tubes. The means which is responsive to the large-amplitude impulses only is effective to send an impulse to the routing control tubes to cause one-of these tubes to be fired ea h time a large-amplitude impulse is received in the receiving apparatus.

The operation of the receiving apparatus is as follows:

The receiving apparatus is prepared for the reception of data by causing the presetting tube of each bank of transforming and symbol-storing tubes and the first tube in the routing control device to be fired and rendered conducting.

The firing of the presetting tube in each bank of transforming and symbol-storing tubes will, through the mutual extinguishing connections, clear these banks of any previously stored symbols, and the firing of the first tube in the routing control device will likewise cause any other tube of the device to be extinguished and insure that the first entry will always be routed to the first bank of transforming and symbol-storing tubes.

The conducting presetting tube of each bank will prepare the marking impulse tube in its bank of tubes to be responsive to signal impulses and will continue to be conductive until signal symbol impulses are relayed to that bank and cause the marking impulse tube therein to be fired and rendered conducting.

The conducting routing control tube renders the relay means for the first bank effective and prepares the routing control tube for the second bank for firing in response to the first large-amplitude impulse to be received.

The receiving device is now ready to receive signals. As the first burst of impulses is received, the small and large-amplitude impulses will be passed on to the common impulse lin and relayed from the common impulse line to the first bank of transforming and symbol-storing tubes, and these tubes will be operated one after another in response to these impulses, the last tube to be operated being the symbol-representing tube corresponding to the symbol represented by the burst; The marking impulse, or large-amplitude impulse, which is the last impulse of the burst, will also be effective, through the discriminating means, to cause an impulse to be sent to the routing control tubes. The routing control tube for the second bank has been prepared for firing by the conduction in the first tube, and, when' the impulse is sent to these tubes in response to the marking impulse of the burst, the second 'bank routing control tube is fired and rendered conducting.

the second bank of transforming and symbolstoring tubes operative.

The next burst of impulses will cause the transforming and symbol-storing tubes of the second bank to be fired to set up and store the symbol represented by the second burst of impulses. As before, the last or marking impulse of this burst will cause the firing of the next routing control tube and prepare the next transforming and symbol-storing bank for reception of the next burst of impulses. In this way, the successive bursts of impulses are routed to the various banks of symbol-storing tubes and control the setting of the various symbols therein.

After the sequence of bursts have been received, th conducting tubes representing the symbols in the various banks can be used to control an indicating means or a recording means or can be used to control the transfer of the symbols directly to other storing means for future use.

The invention is not limited to the use of a multiple-bank sending apparatus, because a single bank could be used repeatedly to send out successive bursts of impulses which the receiving apparatus would allocate and transform into successive settings representing the symbols in the same manner as explained above for the fivesymbol sequence. Nor is the receiving apparatus limited to five banks of transforming and symbol-storing tubes, as it is obvious that more banks of transforming and storing tubes could be used if it were desired to increase the capacity of the receiving apparatus.

Thus it is seen that applicants have provided a novel communication system for sending and receiving data at a high rate of speed.

DETAILED DESCRIPTION Sending apparatus The sending apparatus is shown in Figs. 1 to 6 inclusive.

The disclosed embodiment of the invention is adapted to send five symbols automatically in succession in the form of bursts of impulses, Fig. 15 shows, in a general way, a train of impulses made up of the bursts of impulses which would be used to transmit the sy bols for A, Space, "C," yn d A consideration of these bursts shows that the "space" symbol is represented by a burst containing one small-amplitude symbol-representing impulse followed by a large-amplitude marking impulse; the letter A is represented by a burst containing two small-amplitude impulses and a large-amplitude impulse; and the letter B is represented by three small-amplitude impulses and a large-amplitude impulse. In the instant embodiment, this relation between the various letters and the number of small-amplitude impulses extends to the letter Z, which would be represented by twenty-seven small-amplitude impulses and a large-amplitude impulse.

The form of the impulses as shown in this figure is one form which may be used, but the invention may b carried out with other forms of impulses just as long as a distinction is maintained between the variable number of impulses 8 and the marking or controlling impulses. The numerals I. an." n, v, and V i d t the order in which the symbols are transmitted, and similar numerals will be applied to the parts of the sending and receiving apparatus which deal with these symbols. a

Symbol-transforming means Five banks of key are provided for setting up the symbols, and associated with each bank is a. symbol-transforming 'control means which controls the transformation of the symbols into diii'erent numbers of impulses. The banks are shown in Figs. 1 to 5 inclusive, and, as the banks are substantially alike, it is believed that the operation of all the banks will be clear from a description of the elements of one bank and their operation.

It is not intended that the invention be limited to the use of the particular potentials and values of resistance and capacitance given in the following description, because the potentials applied to the various elements of the tubes are merely selected as convenient potentials for the disclosure, and the circuit elements of resistance and capacitance correspond in relative value to the potentials chosen. It is obvious that other potentials may be used and the values of the circuit elements adjusted according to maintain the proper relation between the various parts of the circuit. Throughout the drawings the cathode heater elements are shown conventionally.

Referring to Fig. l, which shows a symboltransforming means for the first symbol to be transmitted, it will b seen that the symbol-transforming means is made up of a plurality of gaseous electron tubes. The tubes are of the type having an internal potential drop of about 15 volts when conducting and having an anode, a cathode, and a control grid which is given a, negative bias with respect to the cathode and will prevent the tube from firing until this bias is reduced to less than 15 volts negative with respect to the cathode. The tubes making up the bank fall into three classificationsnamely, symbol-representing control tubes; a marking impulse tube; and a shift tube.

As many symbol-representing control tubes will be included in each bank as there are symbols which may be selected for transmission, and these tubes will control the creation of difierent numbers of impulses by which the symbols are represented. In the present embodiment, each group will include a tube for a "space" symbol and one for each of the letters of the alphabet, though in Fig. 1 only the Space, A," B, Y, and Z tubes are shown, the symbol-representing control tubes for the leters "C to X inclusive having been omitted to simplify the showing of the bank because the circuits for these tubes ar identical with those of other symbol-representing control tubes and the operation of the symboltransforming means can be readily understood without a showing of them.

, One marking impulse tube Mark" is provided for the bank and is operated to control the creation of a marking impulse for indicating the end 9 impulses after the marking impulse tube of one bank has operated to cause a marking impulse to be created to indicate the completion of the symbol-representing burst of impulses.

The circuits for supplying potential to the elements of the symbol-representing control tubes and for interconnecting these tubes for sequential operation are similar for all these tubes and will 63 over resistor 64 of 150,000 ohms, point 65, a

resistor 66 of 75,000 ohms, points 61 and 60, and

over resistor 69 of 15,000 ohms and capacitor I0 of .002 microfarad in parallel, to ground.

The cathode II of the A tube is connected to this circuit at point 61 and has a negative potential of approximately 9 volts when the tube is not conducting. When the tube is conducting, the cathode is also conductively coupled to its related anode'by the discharge path through the tube, so that the positive potential which is applied to the anode will also be impressed on the cathode potential supply circuit and will cause the potential of the cathode to rise from a negative potential of 9 volts to a positive potential of about '70 volts.

Each cathode potential supply circuit is utilized to supply negative biasing potential for the control grid of the next tube in the sequence, which is, in this case, the Space" tube. From the point 65 in the cathode circuit for the A tube, the circuit extends through point I2, over resistor I3 01" 500,000 ohms, point I4, a resistor 15 of 50.000 ohms, to the control grid I6 of the "Space? tube and provides this gridwith a negative biasing potential of approximately 56 volts. This connection between the cathode circuit of one tube and the control grid of the next adjacent tube of the series enables the potential rise of the cathode of one tube to reduce the bias of the control grid of the next tube in the sequence to a value below its critical potential and will cause the next tube to automatically fire and become conducting.

Since the Z tube is the first tube in the sequence, the control grid ll of this tube is given a biasing potential of the same value as the grids of the other tubes by means of a circuit which is equivalent to the other cathode potential supply circuits and extends from the negative potential supply line 6|, over point I9, resistor I9 of 150,000 ohms, point 80, and resistor 8| of 90,000 ohms to ground, to which circuit the grid I1 is connected from point 80 over resistor 82 of 500,000 ohms, point 83, and resistor 84 of 50,000 ohms.

Each control grid of the symbol-representing control tubes is electrostatically connected to a starting impulse conductor 90, the connection for the grid I6 of the Space tube extending from point 14 in the grid circuit, over a capacitor 9| of 10 micro-microfarads to the conductor 90. The starting impulses, which are positive potential impulses impressed on conductor 90, tend to reduce the negative bias of the control grids below their critical value, but are not suiilcient to overcome the normal negative bias. The starting impulse will be effective to cause a tube to be fired only if that tube has been.primed" or has its grid bias reduced to near the critical point so that the starting impuls can reduce the bias below its critical point and cause the tube to fire and become conducting. The manner in which the tubes can be primed will be explained hereinafter.

Positive potential is supplied to the anodes oi the'symbol-representing control tubes by a. circuit which extends from terminal 92 (Fig. 6), upon which is impresseda positive potential of 105 volts, and continues over conductor 93, point 94, conductor 95, points 96 and 91, a resistor 99 of 500 ohms, point 99, a resistor I00 of 3,000 ohms,

point IOI, and conductor I02 to the common anode potential supply terminal I03 for the symbol-representing control tubes.

Point 99 in this circuit is connected to ground over a capacitor of 0.1 microfarad, which absorbs the shock of any abrupt potential application or change in the circuit.

Terminal I03 is connected to terminal I 04 (Fig. 1), to which is connected an anode potential supply conductor I05 for the symbol-representing control tubes of this bank. Each of the anodes of the symbol-representing control tubes of this bank is connected over a resistor of 1,000 ohms to the anode potential-supply conductor I05, as, for instance, resistor I06, over which the anode I01 of the A" tube is connected to the anode potential supply conductor I05.

When none of the symbol-representing control tubes is conducting, a positive potential of 105 volts is applied to the anodes; however, when one of these tubes is conducting, the potential will be reduced to about 85 volts due to the drop across the resistors 99, I00, and I05..

At the moment one of these tubes is fired, its cathode will remain at a negative potential of 9 volts while the capacitor, as I0, is charging, and, due to the resistance in thecommon anode potential supply circuit for the symbol-representing control tubes and the internal potential drop of the tube, the potential of the anode will drop to within about 15 volts of the cathode potential. This will cause a drop in potential of the anode potential supply conductor I 05, which drop provides a negative potential impulse on the conductor. As the anodes of all the symbol-representing control tubes of a bank are connected to the anode potential supply conductor I 05, a series of negative impulses will be impressed on the conductor as these tubes are fired one after another. These impulses are used to control a signal-generating tube I45 (Fig. 6), which, in a manner to be described later herein, creates symbol-representing impulses corresponding in number to those required to represent the symbol being transmitted.

The drop in the potential of the anode potential supply conductor I05 is also used to extinguish any previously conducting tube which has its anode connected to the common source of anode potential for the symbol-representing control tubes, which includes the resistors 98 and I00. The extinguishing action occurs because the potential of all the anodes of these tubes will drop as the potential of the anode supply conductor drops, and this will cause the potential of the anode of a previously conducting tube to drop below the potential of its cathode, which has risen due to conduction in the tube, and will cause conduction to cease in that tube and enable the control grid to regain control.

Negative potential is applied to the cathode 11 I of the marking impulse tube "Mark by means of a circuit similar to the ones for the symbolrepresenting control tubes, the circuit for the marking impulse tube extending from the negative potential supply conductor 0| at point I03, over resistor H0 at 150,000 ohms, point III, resistor II2 oi 75,000 ohms, point I I3, and over a resistor II4 of 15,000 ohms and a capacitor II! of .002 microtarad in parallel, to ground, to which circuit the cathode I03 of the marking impulse tube is connected at point II3. As in the case of the symbol-representing control tubes, the oathode of the marking impulse tube will acquire a positive potential when the tube is conducting.

Negative bias for the control grid N6 of the marking impulse tube is obtained by connecting the control grid to point III in the cathode potential supply circuit for the "Space" tube. This connection enables the potential rise of the cathode of the Space" tube to be reflected on the grid of the marking impulse tube and cause the negative bias to be reduced below the critical point and the tube Mark to fire and become conducting automatically after the "Space" tube has become conducting.

The control grid of the marking impulse tube has no connection to the starting impulse conductor 30 and accordingly can be fired only when conduction occurs in the last symbol-representing control tube of the sequence, which in the instant embodiment is the Space" tube. I

The potential supply circuit for the anode of the marking impulse tube is similar to that for the symbol-representing control tubes. The circuit extends from the terminal 02 (Fig. 6), upon which is impressed a positive potential of 105 volts, conductor 93, point 94. conductor 05, point 38, resistor H3 of 500 ohms, point IIO, resistor I20 of 4,000 ohms, point I2I, and conductor I22 to common anode potential supply terminal I23 for the marking impulse tubes. Point H8 in this circuit is connected to ground over a 0.1 mircrofarad capacitor, which absorbs the shock of any abrupt application or change of potential in this circuit. Terminal I23 is connected to terminal I24 (Fig. 1), to which is connected the anode I25 of the marking impulse tube of this bank. The anode I25 will have a normal positive potential of 105 volts, but, due to the resistance in the common anode potential supply circuit, this potential will drop as the tube is fired and will fluctuate in a manner similar to that described above for th'esymbol-representing control tube; namely, drop to a positive potential of about 6 volts while capacitor Iii is charging and then rise to about 85 volts as long as the tube is conducting. The potential drop which occurs while the capacitor H is charging provides a negative potential impulse which is used to control a signal-generating tube I46 (Fig. 6) for creating a marking signal in a manner to be described later herein. This impulse, which occurs at the moment the marking impulse tube is fired, can also cause any other tube which is connected to the common anode potential supply circuit for the marking impulse tubes, over resistors H0 and I20, to be extinguished. It should be noted that, since the symbol-representing control tubes have a different anode potential supply circuit from the marking impulse tube, the firing of the marking impulse tube will not be effective to extinguish the last symbol-representing control tube of the sequence which has been fired and is conducting.

The cathode I20 of the shift tube is connected to ground from point I2'I over a resistor I23 of 45,000 ohms and capacitor I23 of .002 microfarad in parallel. The cathode, therefore, is normally at ground potential, but, when the tube becomes conducting, the potential of the cathode rises due to the resistor I20. A conductor I30 extends from the cathode circuit at point I21 to the terminal I3I to enable the potential rise of the cathode I26 to be used as a starting impulse for starting the firing of symbol-representing control tubes in bank III.

The control grid I32 of the shift tube obtains its negative bias from the cathode potential supply circuit for the marking impulse tube. The connection is from point III in the cathode potential supply circuit of the marking impulse tube and over point I33 and resistor I34 of 500,000 ohms to the control grid I32. The potential rise of the cathode of the marking impulse tube, when that tube is conducting, is effective to reduce the negative bias on the control grid I32 and cause the shift tube to fire and become conducting. A capacitor I35 of .001 microfarad is connected between point I33 in this circuit and ground to delay potential rise of the control grid I32 and the consequent firing of the start tube after the firing of the marking impulse tube. This provides a time interval between bursts, which interval may be made longer or shorter as desired by varying the capacity of capacitor I 35.

Potential is supplied to the anode I30 01 the shift tube by a circuit which starts at the terminal I31 (Fig. 6) which has a positive potential of volts impressed thereon, and continues over conductor I30, point I39, resistor I40 of 500 ohms, point I, and resistor I42 of 4,000 ohms to the common anode potential supply terminal I43 for the shift tubes. Point I in this circuit is connected to ground over a capacitor of 0.1 microiarad. Terminal I43 is connected to terminal I44 (Fig. 1), to which the anode I38 of the shift tube is connected. As in the case of the anodes of the other tubes of thebank, the potential of the anode will drop to about 15 volts above ground, the potential of the cathode, while the capacitor I29 i charging, and this potential drop will be effective to extinguish any Previously conducting tube which derives its anode potential over the resistors I40 and I 42 (Fig. 6) in the common anode potential supply for the shift tubes. Since the anodes of the marking impulse tube and the symbol-representing control tubes have diflerent anode potential supply circuits from that of the shift tube, the firing of the shift tube will be inefiective to extinguish the marking impulse tube or the Space tube.

The sequential and automatic firing of the tubes of a bank always begins with a symbol-representing control tube and is initiated by a starting impulse. The control grids of the symbol-representing control tubes are .electrostatically connected to the starting impulse conductor 90, but are normally sufllciently negatively biased so that a starting impulse impressed on the conductor will not be efi'ective to reduce the bias below its critical point to cause the tubes to be fired and rendered conductive. In order that a starting impulse will be eifective to fire a tube, the tube must be "primed by having the normal bias of its grid reduced to such a degree that the starting impulse will be sufiicient to carry the bias below the critical value and cause the tube to fire and become conducting; accordingly, the selection of 

